An optical assembly applicable to the optical communication system generally includes, as shown in FIG. 4, a sleeve member 2, an optical device, and a joint sleeve (hereafter denoted as J-sleeve). The sleeve member guides an optical ferrule attached in a tip end of an external optical fiber to couple the external optical fiber with the optical device. The optical device 3, which converts signals between an electrical form and an optical form, is inserted into the J-sleeve 4 to couple with the external fiber. The J-sleeve 4 makes the optical device 3 optically coupling with the sleeve member 2.
The optical alignment of the optical assembly 1 shown in FIG. 4 may be carried out by s steps, one of which is the alignment along the optical axis Z and the other is the alignment within the plane perpendicular to the optical axis Z. The former alignment, which is often called as the Z-alignment, is performed by adjusting an insertion depth of the optical device 3 within a bore 4c of the J-sleeve 4. Because the outer diameter of the optical device in the cap 3a thereof is slightly smaller than a diameter of the bore 4c, the adjustment of the optical device 3 within the bore 4c along the optical axis Z may be easily carried out.
The latter alignment, which is often called as the XY-alignment, may be performed by sliding the sleeve member 2 on the flat end 4b of the J-sleeve 4. Because the stub 2b in the center of the sleeve 2a and the holder 2c that press-fits the stub 2b therein and is press-fit within the gap between the cover 2d and the sleeve 2a; the lateral movement of the sleeve member 2 on the flat end 4b of the J-sleeve 4 is equivalent to move the sleeve 2a and the stub 2b with respect to the longitudinal axis of the optical device. Thus, the XY-alignment between the sleeve 2a and the optical device 3 may be performed.
The XY-alignment described above is often carried out by two procedures, one of which is the rough alignment and the other is fine alignment. The rough alignment moves the sleeve member 2 widely in a region on the flat end 4b to estimate a position where a maximum optical coupling efficiency between the sleeve member 2 and the optical device is obtained; then, a fine alignment is performed to slide the sleeve member 2 finely from the position above to find the optimum point at which the optical coupling efficiency between two members, 2 and 3, becomes maximum. Because the Z-alignment shows a larger tolerance compared to the XY-alignment, the Z-alignment is generally performed after the XY-alignment and two members, 2 and 3, are permanently fixed by, for instance, the YAG laser welding. The optical device 2 is fixed to the J-sleeve 4 by the laser welding or the like.
The rough alignment between two processes generally takes a dominant tact time. That is, the rough alignment often adopts, what is called, the spiral alignment as shown in FIG. 5 where a starting point P0 where a substantial coupling is available is empirically selected first; then the sleeve member 2 is spirally moved in counter clockwise as tracing concentric squares to find the position where a maximum coupling is obtained.
However, the spiral alignment above described often causes a rotation of the J-sleeve 4 with respect to the optical device 3. When the optical assembly 1 implements the optical isolator 5, especially in a case where the optical isolator is assembled in the J-sleeve 4, the rotation of the J-sleeve 4 during the rough alignment misaligns the optical isolator 5 with the polarization direction of the LD 3c. The LD 3c has the polarization direction of the light emitted therefrom in parallel to the stacking direction of the semiconductor layers when it has a type of the edge-emitting arrangement. Thus, the un-intentional rotation of the isolator around the optical axis Z may lower the optical coupling efficiency between the optical device 3 and the external optical fiber set in the optical sleeve 2a. The present invention is to provide a method to align the J-sleeve 4 with the optical device 3 without inducing the rotation thereof.